This invention relates to an exhaust control valve system for a parallel multi-cylinder, two-cycle engine and more particularly to an improved exhaust control valve system for such an engine that permits a compact engine construction and near optimum running under all engine conditions.
As is noted in our copending application of the same title, Serial No. 07/566,968, filed Aug. 13, 1990, and assigned to the assignee hereof, the performance of an internal combustion engine operating on the two-cycle, crankcase compression principle can be improved through the use of an exhaust control valve that changes the port configuration and timing in response to engine running characteristics. That is, it is desirable to provide a large overlap to achieve high speed performance but such large overlaps reduce the performance at low and mid ranges. The use of an exhaust control valve can change the timing of the exhaust port so as to optimum at all running conditions.
In connection with the application of this principle, however and as noted in our aforenoted copending application, the positioning of the scavenge and exhaust ports can give rise to greater than desired engine length with inline engines. As also noted in that application, this problem can be overcome by rotating the ports about the cylinder bore axis so as to permit the ports of adjacent cylinders to nest between each other and thus reduce the engine length. However, this means that the exhaust port will then not extend in a direction perpendicularly to a plane containing the cylinder bore axes but is disposed at an acute angle to such a perpendicular plane. In the copending application, the control valves for the exhaust ports are mounted on shafts that extend perpendicularly to the center line of the exhaust passages and thus will provide a symmetrical port configuration regardless of the degree of opening or closure of the exhaust control valve.
The construction as employed in our aforenoted copending application, however, presents certain difficulties in valve actuation. Since the shafts are all parallel to each other rather than aligned, a somewhat complicated arrangement must be employed so as to insure that all valves will be positioned similarly in response to the varying engine condition. Although it is possible to achieve this result, the structure for doing so tends to become complicated.
It is, therefore, a principal object of this invention to provide an improved and simplified and yet compact control valve arrangement for the exhaust ports of a multiple cylinder, two-cycle internal combustion engine.
It is possible to provide an exhaust port configuration as described in our aforenoted copending application and wherein all of the control valves are affixed to a common shaft which does not extend perpendicularly to the axis of the exhaust ports. However, when this is done, the movement of the control valve element will cause a variation in the configuration or symmetry of the exhaust port depending upon the position of the control valve member. This can give rise to less than optimum performance.
It is, therefore, a further object of this invention to provide a control valve arrangement for the exhaust port of a two cycle internal combustion engine of the type wherein the axis of rotation of the control valve does not extend perpendicularly to the axis of the exhaust port and wherein the exhaust port and control valve are configured so as to minimize the amount asymmetry that occurs during the pivotal movement of the control valve.
It is, therefore, a still further object of this invention to provide an improved control valve arrangement for a multiple cylinder inline, two-cycle, crankcase compression engine having angular disposed exhaust passages and control valves that are operated by a common shaft that extends in a non-perpendicular relationship to the exhaust passages and wherein in at least one operative position of the control valve the exhaust port is symmetrical.